The invention relates to a semiconductor module comprising one semiconductor chip which at its back side is connected directly or indirectly to a heat dissipating conductor unit (or heat sink), such as a metal heat spreader plate.
Such a semicondutor module, also called a multichip module, is generally known. In such semiconductor modules the transfer of heat generated in the device in operation commonly presents a problem. Each chip consisting of, say, monocrystalline silicon with dimensions of about 0.5-1 cm square and a thickness of some tens to several hundreds of microns, as a rule contains a few million transistors generating heat in operation. The transistors generally are positioned in or near one main surface of the chip. The removal of heat is to take place from the side opposite to the main surface. What solutions have been found so far for dissipating heat in multichip modules are described in detail in the article "Thermal Management of Air- and Liquid-Cooled Multichip Modules" in IEEE Transactions on Components, Hybrids and Manufacturing Technology, Vol. CHMT-10, No. 2, June 1987, pp. 159-175. Said article shows that more satisfactory results are attained using water cooling than using air cooling, which is not inconceivable considering that air is essentially a poor coolant. Nevertheless, preference is often given to air cooling on account of the medium' s superior handleability.
The invention has for its object to provide a semiconductor module of the type described in the opening paragraph constructed so that superior cooling to that of the known modules is made feasible and even in air cooling more favourable results are attained than could previously be obtained using water cooling.
The semiconductor module according to the invention is comprised of a heat dissipating conductor unit at the side facing away from the chip, said heat dissipating conductor unit being provided with a plurality of projecting closely spaced wire cooling fins of a high thermally conductive material, such as metal, said cooling fins positioned in groups separated from each other by interspaces, which interspaces are connected alternately to an inlet or an outlet for the coolant.
It should be noted that the use of metal wires in heat removal is known in itself. Thus, European Patent Application 082 051 describes a system for cooling electronical elements comprising a pattern of open coils of copper wire soldered to the heat sink of the element formed by a metal sheet. After fixation of the coils they may optionally be cut open, so as to leave a number of loose wires.
From U.S. Pat. No. 4,450,505 a multichip module is known, where at the chips' back side bellows are fixed which are in connection with a space through which a coolant may be passed. A plurality of heat conducting strands extend from the bottom of each of the bellows and hence from a chip's back side into the space for the coolant.
Japanese Patent Application No. 58-200 560(A) describes a system for transferring heat from the chip to the heat sink by means of a flexible wire group that cannot transfer shearing stresses.
IBM Technical Disclosure Bulletin Vol. 21, No. 5, October 1978 (New York, USA) in its article "Brush-tipped Piston for Thermal Conduction" by R. G. Dessauer et al. (p. 1857) describes a different system, in which heat from a chip is transferred by way of the free ends of a bundle of wires of which the other ends are fixed in a spring pressure piston.
In Netherlands Patent Specification 110 715 is described a semiconductor body positioned in a housing and fitted with electrodes, in which the electrode heated most during operation has satisfactory thermally conductive contact with the housing which is of metal at least at the place of contact, with heat being dissipated across a layer of electrically insulating material provided between the metal housing and another component of metal. The construction in this case is such that the insulating layer of synthetic material, which contains, in a manner known in itself, grains of a powdered, high thermally conductive solid insulator, has a plurality of grains of about equal size, with such a small space being chosen between the metal components that the relative distance between the two metal components separated by the insulating layer is equal to the size of these grains.
Electronics & Power, Vol. 18, June 1972 (Hitchen, the article "Spherical Diamond Heatsinks" (see p. 235) notes that diamond particles are electrically insulating and thermally conductive. Because of these properties it is proposed that diamond particles provided in a substrate be used in a heatsink in printed circuits with electronic components.
In EP A 0 065 686 a power device module is described with a dielectric substrate provided between the power device and the heat exchanger containing cooling ribs of aluminium. The dielectric substrate is attached to the aluminium heat exchanger with a structural adhesive containing a thermally conductive filler selected from the following group of materials: powdered aluminium, powdered copper, powdered silver, and powdered beryllia.
None of the aforementioned publications disclose a structure in which metal wires are assembled into appropriately shaped groups which are connected to metal foil baffles arranged in an appropriate pattern, as in the present invention.